The present invention relates to an optical disk recording method and apparatus for recording information on an overwritable optical disk, such as CD-RW, DVD-RAM or DVD-RW, and more particularly relates to a method and apparatus for optical disk recording by a proper writing power at either of the time of initial writing and the time of overwriting.
To compensate for a peculiarity of a disk medium, characteristics of a laser diode (LD) and variations in an optical power of LD, and to perform recording with the optimum optical power, an optical disk recording apparatus executes OPC (Optimum Power Control) to acquire the optimum power for the medium beforehand. CD-RW uses a γ method as OPC. That is, test writing of test data is carried out while changing a writing power of an LD step by step at a predetermined recording speed (linear velocity) by using a PCA (Power Calibration Area) located typically in the innermost track of an optical disk. Upon reproduction of the test data, if a reproduction signal (EFM signal) has a waveform as shown in FIG. 9, a modulation degree (Modulation) m11 is determined from the following equation 1:m11=I11/Itop  [Eq. 1]
Here, Itop denotes an amplitude to a peak value P from an EFM reference level, and I11 denotes an amplitude equivalent to a difference between the peak value P and a bottom value B. The modulation degree m11 is acquired with each writing power and its normalized slope γ is determined from the following equation 2:γ=(dm11/dP)/(m11/P)  [Eq. 2]
The determined m11 and γ may have characteristics as shown in FIG. 10. As the writing power increases, m11 increases gradually and γ decreases gradually. Provided that the writing power at which a γ target is obtained is a Ptarget, optimal writing power Po is determined from the following equation 3:Po=Ptarget×ρ  [Eq. 3]
Here, the parameter ρ is used to calculate the optimal writing power Po from the Ptarget. The optimal writing power Po can minimize jittering at the time of initial writing. Such a value of the parameter ρ only exists one for each medium and each recording speed.
With respect to CD-RW, however, there may be a case where an overwriting characteristic is present and the optimal writing power which has been determined by the γ method should not necessarily be the optimal value for minimizing of the jitter indicative of recording quality. It is seen from FIG. 10 that the writing power at a bottom point of the jitter at the time of initial writing indicated by a broken line obviously shifts from another bottom point of the jitter at the time of DOW1 (Direct Over Write Once) indicated by a dot-dash line. In this case, it can be said that executing OPC makes the recording quality rather poor, and causes a recording quality detarioration that should not be ignored.